I have a Drupal website serving mobile pages from different urls (starting from /mobile). According to Google recommendations I should use the canonical tag to map desktop and mobile pages. Right now I did this in case I serve the same node (e.g: node/123 and mobile/node/123) but should I do this for other pages as well that are equivalent but share a different content? For example do I need to map the desktop and mobile homepages even if they don't have the same content at all?